Hi, like we can do on Dynamics 365 Entreprise, I think it's a good idea to offert the option to choose the URL we want for the Financials tenant.  When we sign in to try it, the system take by default the default Office 365 domain, if it's not the desired domain we can't change it.

Same if have to seperate on company to the other, we can't change the URL.

Please looking to add this option.